The present invention relates to air guns in marine seismic operations. More particularly, the present invention relates to a dual shuttle air gun that centers the air gun shuttles after compressed air in the gun is discharged.
Marine seismic operations record acoustic waves reflected from the sea floor and underlying geologic formations. The acoustic waves are generated by air guns that release air compressed between 2000 and 6000 psi. The acoustic pulse generated by a single air gun is magnified by additional air guns in a seismic array to produce large acoustic waves. These acoustic waves are reflected from the sea floor and geologic formations and are sensed by recording instruments having transducers for converting the acoustic waves into electrical signals. These signals are recorded and subsequently processed to model the subsurface geologic formations.
Conventional air guns store compressed air in a housing that is released through valved ports in the housing. The released air forms a bubble in the water to create an acoustic pressure pulse. An electrically operated solenoid controls the operation of the valves and release of compressed air. One example of an air gun is shown in U.S. Pat. No. 4,623,033 to Harrison, Jr. (1986), wherein an air gun includes valved ports extending 360 degrees around the air gun housing. The port valve comprises a shuttle that reciprocates axially along the air gun.
U.S. Pat. No. 5,365,493 to Harrison (1994) describes an improved air gun that accelerates the shuttle as the air gun is fired. Another air gun design in shown in U.S. Pat. No. 5,001,679 to Harrison, Jr. (1991), wherein the compressed air is released from the housing by the operation of dual shuttles. This dual shuttle concept increases the efficiency of the air gun by expediting the release of compressed air from the housing when the gun is fired. Both shuttles are simultaneously operated to release the compressed air and the shuttles are returned to the original position.
Although improved air guns significantly improve the efficient generation of acoustic waves, the weight and response of air guns can be improved to facilitate the deployment of the air guns and to improve the acoustic wave quality. Accordingly, a need exists for an improved air gun that accomplishes these objectives.